Force Field Analysis for Ethene
The files listed below reproduce the fits given
in Table 2a and Table 2b of L. Hedberg and I. M. Mills, J.
Molec. Spectrosc. 203, 82 (2000). The files are:
- C2H4ff.obs - the observed
quantities for the fit for use with either of the files below.
Points to note:
- Several different (equivalent) ways are used to specify the
- The 13C vibrational frequencies are fitted as
isotope shifts, as these are typically more accurate than
- Different weights (estimated errors ) are used for the
observed values in line with the original paper.
- Coriolis coupling constants for the most abundant isotope
are included in the fit.
- C2H4emp.pgo - a fit to
purely empirical symmetry force constants.
- C2H4scaled.pgo - a fit
scaling ab initio force constants to match experiment.
Notes on the data files:
- The force constants are expressed in symmetry co-ordinates,
rather than internal valence coordinates.
- The definition of the out of plane modes, 7 and 8, seem to be
different from the ones used in the paper.